The invention relates to a safety apparatus for a machine, in which a first machine part performs a working movement towards a second machine part, such as in the case of a press brake.
A known method for non-cutting processing of workpieces is bending or folding. In this case, a workpiece, which is still flat within a region of the processing point at the beginning, is formed under pressure. Used for this purpose during the machine assisted processing are machines which are generally referred to as press brakes in the following. However, the invention is not limited to press brakes in the narrower sense and can likewise be used in folding presses, punching machines, cutting machines and any other kind of machines in which two machine parts perform a hazardous working movement towards one another.
In a press brake, the workpiece is essentially formed by being pressed with a punch against a die. The desired shaping can be achieved by appropriate design of the punch and the die. The punch is often a tool that is arranged on a first, movable machine part, whereas the die sits on a second, fixed machine part. However, since it is only the relative movement of the two machine parts that is the important factor, the die may alternatively also be moved or both machine parts may be moved towards one another. The safety apparatus according to the invention can be used in all of these cases.
It will be readily understood that a press brake poses a considerable risk to the operating personnel, in particular the risk of crushing or even of the risk severing of body parts. Accordingly, it has already been known for a long time to provide press brakes and the like with a safety apparatus in order to avoid accidents as far as possible. For example, a light-grid protection device for a press brake is described in German Patent 852 027, wherein a light-grid protection device with a plurality of individual light beams is arranged in such a way that it moves downwards with the hazardous movement of the first machine part. If one of the light beams is interrupted, the movement of the first machine part is stopped. The light beams of the light grid run in front of and behind the actual working region, i.e. The light grid descends in parallel with the working movement of the first machine part like a type of protective curtain in front of the operator of the machine.
U.S. Pat. No. 5,579,884 discloses a light barrier arrangement in which two or three light beams run parallel to the leading edge of the punch and in advance of the latter. If one of the light beams is interrupted, the movement of the punch stops. If there are only two light beams, they run so as to be offset symmetrically forwards (towards the operator side) and rearward (towards the side remote from the operator). The same applies if three light beams are used, with the third light beam then being arranged exactly below the leading edge of the punch and with a greater advance than the other two light beams. In the arrangement according to U.S. Pat. No. 5,579,884, the third light beam primarily serves as a control beam, which prevents a “muting point” from being set too deep. The muting point determines a point in the sequence of movement of the punch from which the light beams of the safety apparatus are deactivated for a short time period. This is because the actual processing operation could not be completed without such a short deactivation, since the punch is otherwise always stopped when the workpiece to be processed interrupts the light beams.
In a further exemplary embodiment of U.S. Pat. No. 5,579,884, a light grid is provided between the operator and the moving punch in addition to the three light beams mentioned before. This arrangement is specifically provided for the case where the punch has various regions which project to a varying extent in the direction of movement. The light grid is intended to prevent an operator from being able to intrude in a “shorter” section of the punch once the three above mentioned light beams have been deactivated, because a “longer” region of the punch has crossed the muting point.
DE 100 27 156 A1 discloses a safety apparatus for folding presses and the like in which the light beams are deactivated as a function of the speed of the working movement. This known light barrier arrangement contains two or three light beams which essentially run below the leading edge of the punch. A first light beam runs virtually at the level of and in the immediate vicinity of the leading edge, whereas two further light beams are at an increasing distance from the leading edge. In an exemplary embodiment, the light beams further in advance are deactivated one after the other, i.e. At different working positions of the punch.
DE 197 17 299 A1 discloses a safety apparatus having up to four light barriers, the light beam of a first light barrier running at the level of the leading edge of the punch and in the immediate vicinity thereof. The other three light beams form a light grid which is arranged with a certain advance relative to the punch and perpendicularly to the direction of movement, i.e. “horizontally”. The topmost individual light beam serves to adjust the advance of the other light beams with regard to the leading edge of the punch.
WO 97/25568 and WO 00/67932 disclose similar arrangements in which a light grid or light curtain runs ahead of the punch and transversely to the direction of movement of the latter.
DE 27 50 234 discloses a safety apparatus having two light beams in which a first light beam runs ahead of the punch and parallel to the leading edge of the latter, whereas a second light beam is arranged in parallel in the region of the fixed die.
In a safety apparatus according to U.S. Pat. No. 4,166,369, three light beams run with increasing distance in advance of the leading edge of the punch, these light beams being briefly deactivated (muted) one after the other as a function of the respective punch positions reached.
Finally, DE 196 04 900 A1 discloses a safety apparatus in which a plurality of light beams are arranged parallel to the direction of movement of the punch. In contrast to the numerous other examples, however, these light beams do not run with the movement of the punch. Rather, the punch passes through the light grid of the light beams, and a control device deactivates the individual light beams as a function of preset control data records (muting).
Thus, a plurality of the safety apparatuses for press brakes and the like are already known in which light barriers are used in order to detect an intrusion of an operator in the hazardous working region and in order to stop the working movement if necessary. A common feature of all the known arrangements is that the respective light barrier arrangements have to be adapted very exactly to the individual machine, a factor which is quite expensive. In particular the advance of the individual light beams relative to the leading edge of the punch is a critical variable, which in each case has to be matched very precisely to the machine to be protected. Consequently, a considerable outlay is required by the manufacturer and distributor of the known safety apparatuses in order to provide suitable safety apparatuses for various types of press brakes and the like. Only the arrangement disclosed by DE 196 04 900 C2 has a certain flexibility, since adaptation to various machines is possible by corresponding programming of the control device. However, this programming may be very time consuming in an individual case. In addition, this known safety apparatus is based on a fundamentally different concept compared to the other safety apparatuses described before, since the light barriers here, in contrast to the other cases, are arranged in a fixed position.